Although the molecular basis for malignant transformation leading to cancer is not yet fully understood, much information has been developed recently using molecular biology techniques. For example, while it has long been thought that transformation involved the alteration of critical genes, referred to as "oncogenes", such discrete oncogenes have only recently been isolated and shown to cause transformation.
For example, isolated human sequences from the c-K-ras oncogene present in certain human lung tumors have been described. See Nakano, H., Yamamoto, F., Neville, C., Evans, D., Mizuno, T., and Perucho, M., "Isolation of Transforming Sequences of Two Human Lung Carcinomas: Structural and Functional Analysis of the Activated c-K-ras Oncogenes", Proc. Acad. Sci. USA, 81, 71-75, January, 1984; Santos, E., Martin-Zanca, M., Reddy, P., Pierotti, M. A., Della Porta, G., Barbacid, M., "Malignant Activation of A K-ras Oncogene and Lung Carcinoma But Not in Normal Tissue of the Same Patient", Science, 223, pp. 661-4, Feb. 17, 1984. Additionally, an oncogene isolated from the EJ bladder carcinoma cell line has been found to cause transformation when it was transfected into NIH 3T3 cells. See Shih, C., and Weinberg, R., Cell, 29, 161-9 (1982).